Both light water and heavy water reactors produce tritium waste, although more tritium is produced in heavy water reactors by reactions such as D(n,.gamma.)T in the coolant-moderator D.sub.2 O, where tritium concentrations of 6 ppm T:D are common. Tritium concentration in the H.sub.2 O coolant in light water reactors is usually lower by a factor of 10.sup.3 -10.sup.4 than the tritium concentration in heavy water. It is of interest to extract the tritium in an enriched form, both because of the value of enriched tritiated fluids and because of the difficulty of disposal of radioactive, tritium-rich products having a tritium half life of 12.3 years. Twenty years ago, Barr and Drews in "The Future for Cheap Heavy Water", Chemical Engineering Progress 56 (3) 49-56 (March 1960), reported on 98 known processes that promote the separation of the hydrogen isotropes (H, D, T). But not one of these processes is able to economically extract triitium from the process waters of nuclear facilities.
Since 1961, when lasers as substantially monochromatic light sources became available, interest has grown in the use of laser radiation to photoselectively promote chemical reactions. Tiffany, Moos and Schawlow, in Science, 157, 40-43 (July 7, 1967), reported on the use of tunable ruby laser radiation (.lambda.=6934-6943 .ANG.) to photoselectively promote gas phase reactions between Br.sub.2 molecules containing particular isotopes (.sup.79 Br and .sup.81 Br). This may have been the first evidence of photochemical reactions in materials such as bromine in which excited molecules rather than atoms are formed in the primary process. However, when certain isotopes of bromine were photoselectively excited, no net isotopic enrichment was detected in the reaction products, possibly due to isotopic scrambling. This work is discussed further by Tiffany in "Selective Photochemistry of Bromine Using a Ruby Laser", Journal of Chemical Physics, Vol. 48, 3019-3031 (1968).
Robieux and Auclair, in U.S. Pat. No. 3,443,087 (issued May 6, 1969), disclose and claim the use of a narrow bandwidth laser to photoselectively raise an isotope of a given chemical element to an excited state while leaving other isotopes of the chemical element generally undisturbed. The interest of the Robieux et al invention centers on photoselective ionization of the chosen isotope by a two-step laser irradiation process applied to atoms of the selected chemical element.
Nebenzahl and Levin, in German Pat. No. 2,312,194 (issued Mar. 12, 1973), also disclose the use of a two-step laser radiation process to photoselectively ionize atoms or molecules containing a particular isotope such as .sup.235 U. Charge exchange of the ionized isotopes is one of the problems that must be dealt with here.
Mayer, Qwok, Gross and Spencer, in "Isotope Separation with the CW Hydrogen Fluoride Laser", Applied Physics Letters, Vol. 17, 516-519 (1970), discuss the use of a hydrogen fluoride laser (.lambda.=2.64-2.87 .mu.m) to separate deuterium isotopes from hydrogen by photoselective reaction of methanol (H.sub.3 COH) with bromine molecules to form HBr and formaldehyde (H.sub.2 CO). In one approach, methanol with one or more hydrogen atoms replaced by deuterium is caused to preferentially react with bromine by absorption of narrow band laser radiation.
Yeung and Moore, in "Isotope Separation by Photopredissociation", Applied Physics Letters, Vol. 21, 109-110 (1972), discuss photoselective predissociation of H.sub.2 CO to form the products H.sub.2 and CO having a high abundance of preselected isotope-containing molecules such as .sup.13 C, .sup.14 C, and .sup.18 O. Yeung et al also suggested the use of substituted formaldehydes such as Cl.sub.2 CO and Cl.sub.2 CS, for which spectroscopic and photochemical information was not yet available.
Gould, in "Economic Aspects of Tritium Separation from Water via Laser Isotope Separation", thesis for the degree of Nuclear Engineer, M.I.T., February 1978 (unpublished), discusses the possible use of photoselective predissociation of formaldehyde for tritium-from-hydrogen separation.
Jensen and Lyman, in "Laser Induced Recovery of Deuterium or Tritium from Water", Second European Electro-Optics Conference, Montreaux, Switzerland, April 1974, disclosed the use of a two-step selective photolytic process to selectively remove HDO and D.sub.2 O from water, using the coincidence of certain DF laser lines with absorption lines for the desired isotopic molecules. CO is added to the photolysis mixture to remove the O atom from the OH photolysis product, and the desired isotopic material is collected as D.sub.2. Along similar lines, Ambartzumian, Letokhov, et al, in J.E.T.P. Letters 17, 63-65 (1973), used a two-step laser selective photolysis, discussed infra, of the NH.sub.3 molecule to separate the isotopes .sup.14 N and .sup.15 N.
Ambartzumian and Letokhov, in I.E.E.E. Journal of Quantum Electronics, QE-7, 305 (1971), Applied Optics, 11, 354 (1972) and Chem. Phys. Lett., 13, 446 (1972), have reported use of a selective two-step photodissociation process (STP) that uses two simultaneously applied light sources for isotope separation. The first light source, a narrowband infrared laser, selectively excites a predetermined molecular vibration to increase the ultraviolet absorption rate, and the second light source is a continuum ultraviolet source that enhances dissociation of the vibrationally excited molecules.
K. H. Lin, in "Tritium Enrichment by Isotope Separation Technique", Oak Ridge National Laboratory Report ORNL-TM-3976 (December 1972), discusses seven techniques for removal of tritium from an isotope mixture containing H.sub.2 O, HDO, HTO, DTO, D.sub.2 O and T.sub.2 O; using only thermomechanical, mechanical and/or chemical techniques. No laser-assisted techniques are considered.
Kersher and Wadt, in "Laser Isotope Separation: Water Detritiation", Monsanto Research Corp. Mound Laboratory Memo, circa 1975, discuss the possibility of decontamination of tritiated water wastes, using isotope selective vibrational excitation of HTO (but not of H.sub.2 O) to increase the reaction rate of HTO vis-a-vis H.sub.2 O. However, the overall reaction rate of HTO is still quite low as the vibrational energy increase represents only 7-14% of the activation energy for reactions of interest. Therefore, Kersher et al choose the selective two-step photodissociation (STP) process of Ambartzumian and Letokov, supra, applied to the O-T stretch of .nu.'=2,295 cm.sup.-1 (.lambda.=4.36 .mu.m). The photoselective vibrational excitation is provided by a tunable optical parametric oscillator, pumped by a pulsed Nd:YAG laser at .lambda.=1.06 .mu.m. This is followed by application of an intense (.about.2.5.times.10.sup.5 watts/cm.sup.2), pulsed ultraviolet source at .lambda.=1,890 .ANG. (which may be a continuum source) and by provision of a suitable tritium scavenger such as H or H.sub.2. The reactions proceed according to HTO+h.nu..sub.1 (2,295 cm.sup.-1)+h.nu..sub.2 (52,910 cm.sup.-1).fwdarw.OH+T and H+T.fwdarw.HT. These experimental efforts to separate tritium were unsuccessful.
U.S. Pat. No. 4,049,515 to C. P. Robinson et al (issued Sept. 20, 1977) discloses and claims the use of isotope-selective multiphoton absorption of intense, monochromatic light from an infrared laser, such as a CO.sub.2 laser, by a molecular species having a high density of vibrational levels. The molecules containing the predetermined isotope each absorb multiple laser photons and are vibrationally excited to the point that such molecules either dissociate or preferentially chemically react with other molecules to produce dissociation products or reaction products that are isotopically enriched and are easily separated. Robinson et al note that the isotope-containing species is preferably a polyatomic molecule containing four or more atoms, in part to insure a sufficient density of vibrational states.
Benson, in U.S. Pat. No. 4,081,339, teaches the use of organic target molecules of the form RX, with R selected from the ethyl, isopropyl, t-butyl or cyclopentenyl groups and X selected from a functional group including F, Cl, Br, OH (and OD) and H (and D), the molecules being irradiated by a single pulsed infrared laser or by two weaker lasers tuned to photoselectively dissociate the reactant molecules RX containing deuterium in place of one or more H atoms. The dissociation products may be of the form C.sub.n H.sub.2n-1 D+HX and are stable molecules rather than reactive radicals. This process may be of limited utility because of low optical selectivity and severe collisional quenching.
Infrared photolysis of CDF.sub.3, with applications to deuterium separation, has been discussed by Herman and Marling in Chemical Physics Letters, Vol. 64, 75-80 (1979), with CO.sub.2 laser multiple photon dissociation being the moving force. In Jour. of Chemical Physics 72 516 (1980), Herman and Marling show that deuterated fluoroform, CDF.sub.3, exhibits strong, selective absorption peaks at .lambda.=10.21 and 10.31 .mu.m and allows single-step isotopic optical selectivity factors greater than 10,000 at modest pressures. Marling, Herman and Thomas, in Jour. of Chemical Physics 72 5603 (1980) have shown that this process is efficient at pressures of several hundred torr, if one shortens the infrared laser pulse duration to .DELTA.t.ltorsim.2 nsec.
These three reports form the basis of U.S. patent application Ser. No. 943,833 (patent allowed circa July 1980) by Marling and Herman, which discloses and claims the use of intense monochromatic radiation from a pulsed infrared laser, such as the CO.sub.2 laser, to enrich deuterium by selectively dissociating multihalogenated organic compounds such as CDF.sub.3. The cited patent also discloses and claims the use of shortened laser pulse durations (to a few nanoseconds) to permit operation at pressures above 100 torr. Deuterium is replenished in the multihalogenated working molecule by exchange with a deuterium-rich feedstream such as naturally occuring water.
Ishikawa, Arai and Nakane, in Jour. of Nuclear Sci. and Tech. 17 (April 1980) 275, have calculated some fundamental vibration frequencies of twelve halomethanes with tritium substituted at one site for hydrogen (CTF.sub.3, CTCl.sub.3, CTBr.sub.3, CTHF.sub.2, CTHCl.sub.2, CTHBr.sub.2, CTF.sub.2 Cl, CTCl.sub.2 F, CTF.sub.2 Br, CTBr.sub.2 F, CTCl.sub.2 Br and CTBr.sub.2 Cl). These authors use the Wilson FG matrix method, the Urey-Bradley type force and interaction constants of Plyler and Benedict for non-tritium-substituted halomethanes. The authors also assume that substitution of deuterium or tritium for hydrogen would not alter the constants or interatomic distances, and use, as interaction constants for mixed molecules containing more than one species of halogen, the geometric mean of the interaction constants for corresponding molecules containing only one halogen specie. Inherent approximations in this method can produce substantial discrepancies in the frequencies computed. For example, CTF.sub.3 frequencies observed by the applicants herein agree generally with the applicants' own frequency calculations, but differ substantially (by .about.60 cm.sup.-1) with the calculated frequencies of Ishikawa et al. This difference is quite important as the applicants' own calculations, but not those of Ishikawa et al, indicate that laser-assisted isotope separation using CTCl.sub.3 is feasible using a wavelength available from NH.sub.3 laser emission.
Makide et al, in Jour. of Nuclear Sci. and Tech. 17 (August 1980) 645, apply the fundamental frequencies calculated above by Ishikawa et al to multiphoton dissociation of tritium-substituted trifluoromethane, using a CO.sub.2 laser tuned to .lambda.=9.6 .mu.m with a long (100 nsec) pulse duration to separate tritium from hydrogen through reactions such as EQU CTF.sub.3 +h.nu..fwdarw.TF+CF.sub.2, EQU CHF.sub.3 +h.nu..fwdarw.CHF.sub.3 +h.nu..
The observed tritium low enrichment factors (near 10) were low due to their use of a 10 times higher than necessary laser fluence; optimum results occurred for the R(14), 1075 cm.sup.-1 CO.sub.2 laser line, in agreement with earlier calculations and predictions of the applicants herein.